This invention relates to a process which is useful for stably and continuously obtaining a large amount of an aqueous fumaric acid solution and tablets and a column to be used therein. The invention further relates to a deodorization method which is useful in deodorizing bad-smelling components over a long period of time in a toilet, etc.
Compared with other organic acids, fumaric acid exerts a strong antibacterial effect on various gram negative bacteria within a short time. Based on the showing of a strong bactericidal effect on Escherichia coli O-157 which has caused health concerns recently, fumaric acid is expected to be highly useful. In addition, fumaric acid, which is an organic acids contained in natural substances such as rice and mushrooms, is a food additive with no restrictions on use. Thus, it has been employed as a highly safe bactericide.
On the home page (dated Jul. 11, 1997) of Niigata Pref. Central Research Institute, it was reported that a mixture of 0.2% of fumaric acid with 0.2% of ascorbic acid showed a bactericidal effect on salmonella, coliform, enteritis vibrio and yeasts other than gram negative ones. It was also reported that when fumaric acid (0.02 to 0.20%) containing 0.05% of ascorbic acid was compared in bactericidal efficacy with ethanol, ethanol exerted a bactericidal effect after 60 minutes while fumaric acid (0.2%) exerted a comparable effect after 1 minute.
It was reported in xe2x80x9cShoku Ei Shixe2x80x9d (J. of Food Sanitation) Vol. 36, No. 1, p. 50-54 that fumaric acid inhibited the growth of gram negative bacteria; but that fumaric acid was minimally soluble in water at room temperature and a 0.3 % aqueous solution thereof was of little use because of undergoing precipitation at 4xc2x0 C. Further, an aqueous solution of monosodium fumarate having a high solubility did not show bactericidal effects at a concentration of 0.6% or less but rather at 0.8%.
On the other hand, the Journal of Food Protection, Vol. 1, 59, No.4, 1996 (370-373) reported bactericidal effects of organic acids including fumaric acid on various bacteria such as E. coli 0-157. According to this document, fumaric acid exhibited a bactericidal effect exceeding those of other organic acids at 1.0% and 1.5%.
When fumaric acid is used as a bactericide, it has been a practice to dissolve solid fumaric acid in water, etc. to give an aqueous fumaric acid solution. However, fumaric acid shows only a low solubility, i.e., 0.2 to 0.5 g per 100 cc of water at 10 to 20xc2x0 C. The solubility of fumaric acid can be only be minimally improved even at higher temperatures (i.e., 1.6 g at 50xc2x0 C. and 5.25 g at 80xc2x0 C.). Also, fumaric acid has a low dissolution rate. To obtain an aqueous fumaric acid solution, it is therefore necessary to increase its solubility by heating to a definite temperature and then diluting the thus obtained solution, or to forcibly stir the mixture over a long period of time, thus taking a long time and costing much. That is to say, it is very difficult to economically produce a large amount of an aqueous fumaric acid solution within a short time. It is also impossible to obtain an aqueous fumaric acid solution having a high concentration.
Because of the low dissolution rate, fumaric acid cannot be completely dissolved but remains as fine grains giving a slurry in these conventional methods. When 15 g of fine fumaric acid grains (80-mesh pass) are added to 10 l of water at 20xc2x0 C. (i.e., a 0.15% aqueous fumaric acid solution) and slowly stirred for 24 hours, for example, the fine grains are not completely dissolved but partly remain as such. When such an aqueous fumaric acid solution is employed in sterilizing vegetables, etc., the remaining grains adhere to the surface of the vegetables and the fumaric acid at a high concentration causing a partial color change in the vegetables, thus lowering the commercial value thereof. When such an aqueous fumaric acid solution is employed in sterilizing meats, the remaining fumaric acid grains sometimes damage the meat tissue.
A method for obtaining an aqueous fumaric acid solution by adding sodium fumarate or surfactants, which have a high dissolution rate, to fumaric acid having a poor dissolution rate to thereby elevate the dissolution rate as the whole. However, the aqueous fumaric acid/sodium fumarate solution thus obtained is inferior in bactericidal effect to an aqueous fumaric acid solution.
As discussed above, although fumaric acid shows an excellent bactericidal effect, it has low solubility and a low dissolution rate, which makes it impossible to efficiently obtain an aqueous fumaric acid solution having a high concentration (pH 1 to 4).
Granular active carbon and honeycomb active carbon have been employed in eliminating bad-smelling gases in sources and facilities which produce or emit offensive smells, for example, sewage disposal plants, sludge processing plants, fecal disposal plants, cattle farms and garbage processing plants. To elevate the deodorization efficiency, it has been also proposed to use active carbon honeycombs carrying citric acid, alkali metal citrates, etc. thereon (JP-A-59-151963; the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d), honeycombs having acids such as sulfuric acid or alkalis adhered thereto (JP-A-52-63882), honeycombs carrying alkali metal iodides and phosphoric acid thereon (JP-A-6-126166), etc. When these active carbon products are used in deodorizing toilets, in particular, urinals, the deodorizing ability of active carbon is very deteriorated by urinary spray.
Alternatively, aromatic odor-masking agents have been employed in urinals. However, these masking agents cannot deodorize ammonia and amines. Moreover, these masking agents dissolve in urine and thus fail to efficiently eliminate the offensive smells of ammonia and amines over a long time.
Accordingly, an object of the present invention is to provide a process for efficiently producing an aqueous fumaric acid solution having a high safety and an excellent bactericidal effect and tablets and a column therefor.
Another object of the present invention is to provide a process for producing a large amount of an aqueous fumaric acid solution having a high concentration within a short period of time and tablets and a column therefor.
Another object of the present invention is to provide a deodorization method with the use of a solid deodorizing agent which is useful in deodorizing over a long period of time.
Another object of the present invention is to provide a deodorization method which is useful in efficiently deodorizing nitrogen-containing bad-smelling components in a urinal over a long period of time. The present inventors have focused their studies to the fact that fumaric acid shows a very low solubility and a low dissolution rate in water. As the result of intensive studies to achieve the above-described objects, the present inventors have found that an aqueous fumaric acid solution can be stably and continuously obtained by passing water through a column packed with solid fumaric acid. They have further found out that nitrogen-containing bad-smelling components (ammonia, amines, etc.) can be efficiently deodorized over a long period of time by placing a solid preparation containing fumaric acid in a urinal. The present invention has been completed based on these findings.
In the present invention, therefore, an aqueous fumaric acid solution is produced by passing water through a column packed with solid fumaric acid. Water may be passed downward or vice versa. The solid fumaric acid may be in the form of, for example, tablets containing 70% by weight or more (e.g., from 70 to 100% by weight) of fumaric acid.
Although water may be passed through the column, it is also possible to pass an aqueous solution therethrough. The water is not particularly limited and is exemplified by distilled water, purified water, tap water, etc., while the aqueous solution is exemplified by urine, water containing urine, an aqueous solution containing ammonia, etc.
The present invention involves within the scope thereof, a column packed with tablets or solid fumaric acid which are to be used to obtain an aqueous fumaric acid solution.
The present invention further provides a deodorizing agent made of a solid agent containing fumaric acid and a deodorization method. This deodorizing agent, which contains fumaric acid in a solid state, is useful in deodorizing ammonia and amines. In particular, it is placed in a urinal or put into a tank of a tank type flush water closet to thereby deodorize and/or sterilize the same. The deodorizing agent may be in the form of tablets. It usually contains 70% by weight or more of fumaric acid.
Unless otherwise noted, the term xe2x80x9cfumaric acidxe2x80x9d to be used herein involves not only fumaric acid but also fumarates.